1. Field of the Invention
This invention generally relates to optical cables and, more particularly, to a fiber optical plug connector with a mechanism for aligning the core of an optical fiber with a plug microlens.
2. Description of the Related Art
Conventionally, optical fiber connectors are spring-loaded. The fiber endfaces (optical interfaces) of the two connectors are pressed together, resulting in a direct glass to glass or plastic to plastic, contact. The avoidance of glass-to-air or plastic-to-air interfaces is critical, as an air interface results in higher connector losses. However, the tight tolerances needed to eliminate an air interface make these connectors relatively expensive to manufacture.
FIG. 1 is a partial cross-sectional view of a Transmission Optical SubAssembly (TOSA) optical cable plug (prior art). The plug 100 is made from a plastic housing 102 with a bored ferrule 106 to secure an optical fiber 108. The plug 100 also includes a plastic lens 110, manufactured as a subassembly, integrated into the plug. The lens 110 has a curved surface to create a focal plane where the plug mates with a jack 112. The lens permits a low loss air gap to be formed between the plug and a connecting jack. In addition to the expense of manufacturing a 2-part plug, the plug must be made to relatively tight tolerances, so that the lens focal plane aligns with the jack, which also increases the cost of the plug.
FIG. 2 is a partial cross-sectional view of an 8 Position 8 Contact (8P8C) interface (prior art). The ubiquitous 8P8C connector is a hardwired electrical connector used commercially and residentially to connect personal computers, printers, and routers. The 8P8C is often referred to as RJ45. Although the housing/body can be made as a one-piece plastic molding, the spring-loaded contacts and the necessity of cable crimping add to the complexity of manufacturing the part. Advantageously however, the spring-loaded contacts permit the part to be made to relatively lax tolerances.
As noted in Wikipedia, plastic optical fiber (POF) is an optical fiber which is made out of plastic. Conventionally, poly(methyl methacrylate) (PMMA), a transparent thermoplastic (acrylic) alternative to glass, is the core material, and fluorinated polymers are the cladding material. Since the late 1990s however, much higher-performance POF based on perfluorinated polymers (mainly polyperfluorobutenylvinylether) has begun to appear in the marketplace.
In large-diameter fibers, 96% of the cross section is the core that allows the transmission of light. Similar to conventional glass fiber, POF transmits light (or data) through the core of the fiber. The core size of POF is in some cases 100 times larger than glass fiber.
POF has been called the “consumer” optical fiber because the fiber and associated optical links, connectors, and installation are all inexpensive. The conventional PMMA fibers are commonly used for low-speed, short-distance (up to 100 meters) applications in digital home appliances, home networks, industrial networks (PROFIBUS, PROFINET), and car networks (MOST). The perfluorinated polymer fibers are commonly used for much higher-speed applications such as data center wiring and building LAN wiring.
For telecommunications, the more difficult to use glass optical fiber is more common. This fiber has a core made of germania-doped silica. Although the actual cost of glass fibers is lower than plastic fiber, their installed cost is much higher due to the special handling and installation techniques required. One of the most exciting developments in polymer fibers has been the development of microstructured polymer optical fibers (mPOF), a type of photonic crystal fiber.
In summary, POF uses PMMA or polystyrene as a fiber core, with refractive indices of 1.49 & 1.59, respectively. The fiber cladding overlying the core is made of silicone resin (refractive index ˜1.46). A high refractive index difference is maintained between core and cladding. POF have a high numerical aperture, high mechanical flexibility, and low cost.
Generally, POF is terminated in cable assembly connectors using a method that trims the cables, epoxies the cable into place, and cures the epoxy. ST style connectors, for example, include a strain relief boot, crimp sleeve, and connector (with ferrule). The main body of the connector is epoxied to the fiber, and fiber is threaded through the crimp sleeve to provide mechanical support. The strain relief boot prevents to fiber from being bent in too small of a radius. Some connectors rely upon the connector shape for mechanical support, so a crimp sleeve is not necessary.
First, the strain relief boot and crimp sleeve are slid onto the cable. A jacket stripping tool must be used to remove the end portion of the fiber, exposing an aramid yarn (e.g., Kevlar™) covered buffer or cladding layer. Next, a buffer stripping tool is used to remove a section of the buffer layer, exposing the core. After mixing, a syringe is filled with epoxy. A bead of epoxy is formed at the end of the ferrule, and the ferrule back-filled with epoxy. The exposed fiber core is threaded through the connector ferrule with a rotating motion, to spread the epoxy, until the jacket meets the connector. At this point the crimping sleeve is slide onto the connector body and crimped in two places. Then, the strain relief boot can be slide over the crimp sleeve. After the epoxy cures, the core extending through the ferrule is polished with a lapping film. Then, the core is scribed at the point where it extends from the epoxy bead. The extending core portion is then cleaved from the connector and polished in multiple steps.
As noted in the above-referenced parent applications, the advantages of using a microlens in a plug or jack connector include the ability to focus light on point, such as a photodiode or optical fiber core face, while transceiving light in a collimated beam between connectors. However, the focusing of light on a fiber core face requires that the fiber core and microlens be properly aligned.
It would be advantageous if an optical connector plug had a mechanism for self-aligning an optical fiber core with a plug microlens.